BMW N52 fuel and mileage

So according to this thread (https://grassrootsmotorsports.com/forum/grm/the-ultimate-ddd-dads-daily-driver-thats-sub-8k/261474/page1/) I learned that it may not be *that* detrimental to my engine to run 87 octane so since it's winter time up here I decided to give it a try. I track my expenditures via aCar and it breaks a lot of data down. I see no appreciate difference in running 87 vs 93. My wallet, however, is a different story. What's everybody's take on putzing around in 87 octane on an N52? Obviously for summer and track events I'll step it back up but am I good for now? What kind of long-term affects can I expect?

Interested to hear thoughts on this. I have put almost 20k in my N52 but never tried it. 

I doubt you'll have any issues. I've run 87 in the winter in past years and never really saw much difference. In hot weather or hard use, the timing probably gets pulled a bit; I've read suggestions that this also happens in pure highway driving. Given that the only place I've seen notable mileage improvements with 91 is in long highway runs, this could be the case.

I don't use anything other than 93.  I do a lot of highway cruising but I'm at 27mpg including a few track days 

In reply to SKJSS (formerly Klayfish) :

What are you driving to get that fuel efficiency? 

'08 328xi 6spd, 292k miles 

SKJSS (formerly Klayfish) said:

'08 328xi 6spd, 292k miles 

Interesting, that's vastly superior to what I've gotten in either of my E90's, but both were autos - does it make that much of a difference? 

I've noticed issues in the hot summer when I've accidentally used 87. Pulls timing and revs are (I think) noticeably impacted. This is when it's over 100F below the hood of a black 2006 E90. I don't notice a change in mpg (22 city, 28 highway over the last 30,000 miles). 

I posted my experience in the thread you referenced. I'm over 100k miles across 2 different N52 platforms on 87 octane. No issues.

chknhwk said:

SKJSS (formerly Klayfish) said:

'08 328xi 6spd, 292k miles 

Interesting, that's vastly superior to what I've gotten in either of my E90's, but both were autos - does it make that much of a difference? 

Same. I feel lucky if I can get above 19mpg in an X3. 

The higher mpg before August was on a road trip. 

AngryCorvair (Forum Supporter) said:

I posted my experience in the thread you referenced. I'm over 100k miles across 2 different N52 platforms on 87 octane. No issues.

That's good to know. I will start using 91 on my next fill up. 

AngryCorvair (Forum Supporter) said:

I posted my experience in the thread you referenced. I'm over 100k miles across 2 different N52 platforms on 87 octane. No issues.

What has your fuel mileage been?

I do mostly suburban and highway driving with mine.  I "get on it" sometimes, but I'm often lazy and skip shift. 

SKJSS (formerly Klayfish) said:

AngryCorvair (Forum Supporter) said:

I posted my experience in the thread you referenced. I'm over 100k miles across 2 different N52 platforms on 87 octane. No issues.

What has your fuel mileage been?

I do mostly suburban and highway driving with mine.  I "get on it" sometimes, but I'm often lazy and skip shift. 

I skip shift every day, because I hammer it in 2nd and 3rd (E92). From the other thread:

rather than viewing it as "87 hurts fuel economy and power", i look at 87 as baseline and looked for gains with 93.

in my AWD E60 with N52 and automatic, i ran a few tanks of 93 and did the math. I did not gain mpg in local driving, and only gained 10% mpg on highway (from 22 up to 24 iirc).  Not enough to warrant the 25-35% price delta.  i ran 87 in that car from my purchase at 136k until it was totaled at 225k.

in my RWD E92 with N52 and 6MT, i ran a few tanks of 93 and did the math. Again, I did not gain mpg in local driving. On pure highway driving I gained 18% mpg (from 28 up to 33).  Not enough to warrant the 25-35% price delta.  i've run 87 in that car from my purchase at 71k to the current 113k.

Just as another data point, my 128i 6MT seems to average around 23 in mixed driving, with 28-29 consistently possible in prolonged highway runs (this is on 91). One additional thing I've noticed that has a significant impact is cold starts.

Dang, I must have a serious case of Pb in the t-o-e.  Either that or the wagon is just that much heavier - I'm simply not getting those numbers for fuel efficiency...

What speed are you guys running in top gear at 2750 and 3000 rpm?

I will check tomorrow, but seem to remember between 75-80 at those engine speeds. 

In reply to Slippery :

I'll have to check the next time I drive mine. I do know that there were a number of combinations of transmission and final drive ratios, depending on which particular model you have. My car has a 0.85 ratio in 6th, and a 3.23 rear end.

I avg 25mpg in my 5 series wagon.  3.0 N52, automatic, driving to get economy (easy on the throttle, maintaining momentum where possible - not hypermiling)

My wife seems to get 22-23mpg, driving differently.

87 octane equivalent

My daily commute is 10 minutes of traffic lights and then two exits on the interstate. I'd get right at 20/21 with my E91 (6MT RWD) on premium. Highway cruise vs traffic makes a HUGE difference with that car. Compared to 'most' cars, 230hp is a decent bit of power, so tapping into that drinks fuel, that's just simple thermodynamics. Cruising at 70mph takes something shy of 20hp. Your personal driving cycle makes a huge difference when talking real-world mpg

This is a really surprising read to me. 

I've never really even considered running lower octane than recommend by the manufacturer. Possibly ruining an expensive engine in order to save a few bucks?

I'm definitely someone who is comfortable with modifications and making different decisions for different tradeoffs than the factory engineers. But for whatever reason fuel (all fluids, really) seems different to me.

If fuel cost matters that much to a driver (which I 100% understand), then shouldn't that kinda be considered before buying the car? And if money really is that tight, potentially ruining the engine seems like an even worse gamble?

So my question to those who run 87 in a car that requires higher, how do you know that you aren't going to damage the engine?

Robbie (Forum Supporter) said:

If fuel cost matters that much to a driver (which I 100% understand), then shouldn't that kinda be considered before buying the car? And if money really is that tight, potentially ruining the engine seems like an even worse gamble?

in both cases (E60 that i ran from 136k to 225k, and E92 that i bought at 71k and has 114k now), i bought the price, not the car.

So my question to those who run 87 in a car that requires higher, how do you know that you aren't going to damage the engine?

all modern engine controls include knock sensing, and i know how to listen to my engines, so i never worried about hurting either car with 87 octane.  i'll consult the E92 owners manual, but i distinctly remember reading something like "if 93 isn't available, you can run 87" or something similar.

Just for simple numbers. Let's say I get about 30mpg and drive about 15,000 miles per year. That's 500 gallons of gas.

87 is about $1 cheaper per gallon than premium. So that's a $500 savings per year.

But how much is a new engine and r&r? $2000? Remember we're talking bmw here. Maybe more like $10,000? 

If I'm gambling a $10k engine to save $500, I need to be pretty sure about the bet beforehand.

In reply to AngryCorvair (Forum Supporter) :

I do get the knock sensing thing. I remember being told by Alfa that knock sensing above about 3k rpm is just a crapshoot because there is so much noise in the engine. I got the sense that knock sensing is not nearly as foolproof as it seems. 

That would be very interesting wording in the owners manual. I'll look at mine closely too.

In reply to Robbie (Forum Supporter) :

I came to your same conclusion today. I probably would save $400 tops/year. Its not worth it to me, even though I doubt the engine will suffer. 

I guess my biggest problem is not being able gas up once a week. I wish the car had a bigger tank. 

I drove my wife's diesel and that thing will do two weeks easy on one tank.